The overall goal of this grant proposal entitled Regulation of Lysosomal cholesterol in Atherosclerosis is to define a novel role of CD38-NAADP pathway in the regulation of lysosomal cholesterol transport in macrophages in atherogenesis. The hypothesis being tested is that a fine regulatory mechanism of lysosome function via CD38-NAADP signaling pathway plays a critical role in removal of free cholesterol from lysosomes in macrophages and that the abnormality of such CD38-associated lysosome regulation contributes to the pathogenesis of atherosclerosis. Three specific aims to be determined are: 1) To determine whether the deficiency of CD38-NAADP signaling pathway contributes to the accumulation of lysosomal free cholesterol and foam cell formation and to explore the underlying mechanisms using primary cultures of macrophages prepared from CD38-/- and wild type(WT) mice~ 2) To determine whether the deficiency in CD38-NAADP signaling pathway in macrophages leads to lysosomal free cholesterol deposition and consequent atherosclerosis in coronary arteries and aorta using bone marrow transplantation model within CD38-/-,TRP- ML1-/- (transient receptor potential-mucolipin 1) and WT mice~ and 3) To examine how the deficiency of CD38 with deranged lysosomes induces dysfunction of macrophages and atherosclerosis and to define the mechanism mediating the actions of accumulated lysosomal free cholesterol in atherosclerosis by transplanting CD38-/- bone marrow into LDLr-/- mice. The findings of this grant proposal will, for the first time link a membrane differentiation antigen - CD38 to the regulation of lysosome function n free cholesterol clearance through its product, NAADP, which as a second messenger regulates lysosome calcium movement. It is predicted that these proposed studies, when completed, will reveal a new molecular signaling pathway contributing to the pathogenesis of atherosclerosis and thereby direct toward the development of new therapeutic strategies for the prevention and treatment of atherosclerosis. Such direct therapeutic manipulation of the CD38-NAADP signaling pathway in regulating lysosomal cholesterol metabolism and transport may pinpoint the atherosclerotic lesions to reverse foam cell formation, which could be more effective in the prevention and treatment of atherosclerosis, compared to current systemic lipid-lowering medications.